(1) Field of the Invention
The present invention relates to a packet transfer apparatus and, more particularly, to a packet transfer apparatus adapted to connect a plurality of IP (Internet Protocol) networks of different address versions.
(2) Description of the Related Art
In a packet transfer apparatus for connecting an IPv4 network in which packet transfer is performed according to an IPv4 address and an IPv6 network in which packet transfer is performed according to an IPv6 address, an address translator function of executing IPv4-IPv6 address translation on a packet sent from the IPv4 network to the IPv6 network and, on the other hand, executing IPv6-IPV4 address translation on a packet sent from the IPv6 network to the IPv4 network is necessary.
The structure of a conventional address translator is designed on the basis of a packet transfer apparatus for use in an IPv4 network of an old address version and the address of a packet received from the IPv6 network is translated to an IPv4 address by providing an interface on the side of an IPv6 network as a new version with an address translating function, thereby performing packet routing in a node.
Specifically, in a conventional packet transfer apparatus, the address of a packet received from the IPv6 network is translated in accordance with an address version of a packet received from the IPv4 network, all of input packets are supplied in the form of IPv4 packets to an internal switch unit, and the address of a switched output packet to the IPv6 network is translated to an IPv6 address by the interface on the IPv6 network side.
In the case where communication is carried out between a first terminal connected to an IPv4 network and a second terminal connected to an IPv6 network, in the packet transfer apparatus for connecting the IPv4 network and the IPv6 network, a virtual IPv6 address is assigned to the first terminal, and a virtual IPv4 address is assigned to the second terminal. In an IPv4 packet on the IPv4 network, the first terminal is indicated by an actual IPv4 address and the second terminal is indicated by the virtual IPv4 address. In an IPv6 packet on the IPv6 network, the first terminal is indicated by the virtual IPv6 address and the second terminal is indicated by an actual IPv6 address. The address translation described above denotes translation between the actual IPv4 address and the virtual IPv6 address and translation between the virtual IPv4 address and the actual IPv6 address.
As a prior art relating to the address translation between IPv4 addresses and IPv6 addresses, for example, Japanese Unexamined Patent Publication No. 2001-285366 proposes, in order to deal with a shortage of the virtual IPv4 address, to search an address translation table on the basis of a combination of an IPv4 address and a virtual IPv4 address as a search key, so that the same virtual IPv4 address is commonly used by a plurality of IPv6 terminals.